Yesterday I drove past the wind turbines near Darling, and on impulse dropped in. A very friendly Dirk Mostert showed me around.

Dimensions: The turbine blades are 29m, and turn at a constant 18rpm, rated at a max of 1.3MW. The blades are fixed pitch, although they can be manually adjusted to different pitches (by shutting down, undoing all the bolts, turning each blade, etc). So, the circumference is 182m, and the swept area 2642 sq.m!

Wind speed: The wind speed when I was there was between 14m/s and 18m/s, so the standard formula, for 14m/s givesP(max) = 0.35 x 2642 x 14 x 14 x 14 = 2.53MW.

Efficiency and Tip Speed Ratio: The turbine was producing 1MW at the time, so was operating at about 40% efficiency.They are different to a small variable speed turbine, in that, due to the fixed RPM (needed for grid synchronisation) the TSR (tip speed ratio) varies with wind speed. At 18rpm, the tip speed is 54.7m/s, so in a 14m/s wind that is a TSR of 3.9, and at 18m/s it is 3.0. Obviously this impacts on the efficiency of the operation of the blade, butt hey have chosen the simplicity and reliability of the fixed pitch design.

Noise: The blades made a wooshing sound as they went past the tower, but even in that high wind it was easy to have a conversation directly below them without raising your voice.

Bird kill: We have all read the disinformation put out about turbines killing birds. In the year and a half of operation there, the number of birds killed has been: zero, zip, nada, 0!

Hi,I saw this project when stage one had just been completed, but at the time there seemed to be a number of problems with it, and the turbines were not turning. From the sounds of things that is all better now, but can you tell me if stage two (I think that was another 6 turbines, bringing it to 10 all together) is operating yet?

That is high. I wonder how well it would work in reverse? My guess it would offer a lot of resistance, and there may be a lot of static friction - i.e. it would need a lot of torque to start it spinning. A worm gear will not work in reverse at all!